In case of manufacturing a semiconductor device, a film forming processing and a pattern etching processing are repeatedly carried out with respect to a semiconductor wafer. Specifications of the film forming processing become stricter every year as the semiconductor device becomes of a higher density and higher integrity. For example, such a very thin oxide film as an insulating film of a capacitor and a gate insulating film is required to be even thinner but with a high insulative property.
A silicon oxide film and a silicon nitride film have been conventionally used as such an insulating film. However, recently, there is a growing tendency of using a metal oxide film, e.g., a tantalum oxide (Ta2O5) film, as a material having more satisfactory insulative property (see, e.g., Japanese Patent Laid-Open Publication No. 1990-283022). Such a metal oxide film, even when it's thin, exhibits a greatly reliable insulative property. In order to form the metal oxide film having satisfactory properties, it is required to control the temperature of the semiconductor wafer accurately during the film forming processing.
Such a metal oxide film may be deposited by way of MOCVD (metal-organic chemical vapor deposition), i.e., by using a gasified organometallic compound. In case of forming a tantalum oxide film by MOCVD, a metal alkoxide of tantalum, e.g., Ta(OC2H5)5 (pentaethoxytantalum: PET), is used as a liquid source. The liquid source is vaporized by bubbling a nitrogen gas therethrough or by a vaporizer in which a vaporization temperature is maintained, and then is transported as gas phase species to a processing chamber kept under vacuum. At the same time, an oxidizing gas such as oxygen gas is provided into the processing chamber as well. The supplied source provides a film forming material as it is decomposed on a surface of the semiconductor wafer heated to a processing temperature of, e.g., about 450° C. The tantalum oxide (Ta2O5) film is deposited on the surface of the wafer by the film forming material.
In a conventional single wafer thermal treatment device for semiconductors processing, a thermocouple serving as a temperature detection means is installed at a susceptor where a wafer is mounted in order to control the processing temperature. The wafer temperature is detected indirectly by the thermocouple. Based on the detected temperature, an output of a heating means such as a heating lamp or a heater is controlled and thus the wafer temperature is controlled. As mentioned above, such a thermocouple directly detects the susceptor temperature to thereby indirectly detect the wafer temperature thereon. Hence, there inevitably occurs a certain difference between the actual wafer temperature and the detected temperature.
Instead of employing the thermocouple, there has been proposed another scheme wherein the wafer temperature is detected by using a radiation thermometer which detects temperature of an object based on a radiation intensity of a specific wavelength band of the object to be measured [see Japanese Patent Laid-Open Publication No. 1996-264472 (pages 4 to 5 and FIGS. 1 and 2) and Japanese Patent Laid-Open Publication No. 1999-45859 (page 4 and FIG. 1)]. By way of using the radiation thermometer, the wafer temperature can be detected directly and accurately in a contactless manner.
In case of using the radiation thermometer, if an extra thin film deposited on an incident plane of a light probe for collecting light emitted from the wafer, the wafer temperature cannot be measured accurately because the thin film absorbs the light. During the process of forming a film on the wafer, therefore, it is required to prevent the thin film from adhering to the incident plane of the light probe exposed to a processing space, or a transparent glass substrate or the like dividing the incident plane from the processing space.
However, if a certain gas is provided to the incident plane, the transparent glass substrate, or the like for the sole purpose of preventing adhesion of the extra thin film, a partial pressure of a source gas (for example, pentaethoxytantalum) required for forming the metal oxide film becomes lowered due to the extra gas. As a result, a thickness of the film where the certain gas is provided is changed and the uniformity of film thickness over the wafer surface is deteriorated.
Furthermore, in case of the processing device using the heating lamp, a certain part of heat rays originated from the heating lamp may undergo scattered reflection in the processing space to finally get into the radiation thermometer. In this case, the wafer temperature cannot be measured accurately.